Near Field Communication (NFC) is a communication technology, which uses an inductive coupling of devices for a wireless interconnection between them. Two devices equipped with NFC technology set up a near-field communication link when their NFC interfaces are positioned close to each other within 20 cm or less or are brought in contact with each other. The NFC interfaces of the devices link up in a peer-to-peer network.
As a wireless communication technology among a multitude of others, NFC has been designed with a view especially to signal and data exchange between consumer electronics devices. NFC technology can for instance be used to exchange configuration data in the process of setting up a longer-range or faster communication link of another technology like Bluetooth or wireless Ethernet. Examples of consumer electronics devices to be equipped with NFC communication capabilities are television devices, radio receivers, stationary or mobile telephones, laptop or handheld computers, or the like. Such devices will also be referred to as communication devices hereinafter, even though their primary function may not always be communication.
NFC communication devices operate at a center frequency of 13.56 MHz. The current NFC protocol is defined by the standard ECMA 340 of December 2002 and will be outlined in the following paragraphs.
A peer-to-peer NFC communication uses a half-duplex communication scheme. That means, at any one time communication is allowed only in one of the two possible directions. For instance, a second communication device initiating the communication (hereinafter also referenced as “initiator device” or “initiator”) sends a request message to a first communication device (hereinafter also referenced as “target device” or “target”). After having sent the request message, the initiator cannot send another request message to the same target before a response message has been received from that target. However, the initiator device can in the meantime communicate according to the same half-duplex scheme with one or more additional target devices, which in the mentioned standard is referred to as a multiactivation mode. On the other hand, a communication device that has taken on the role of a target in an NFC exchange can communicate with only the initiator of that communication. It should be noted that the terms “initiator” and “target” give a functional meaning to the first and the second communication device. This function can change with time so that the first communication device can be target at a first time and initiator at a second time. The same applies to the second communication device accordingly.
According to the NFC standard, two alternative physical communication modes can be used. These modes are known as the active and the passive communication mode, respectively. In the active communication mode, an initiator and a target generate and use their own radio frequency (RF) field to enable communication. The initiator starts the communication. The target responds to an initiator command or request in the active communication mode using a self-generated modulation of the self-generated RF field. In a passive communication mode it is again the initiator that generates the RF field and starts the communication. The target, however, responds to an initiator request using a load modulation scheme, i.e., by modulating the RF field generated by the initiator and without generating its own RF field.
In the exchange of request and answer, the initiator has no timing restrictions, whereas the target has only a limited time span to provide an answer. This time span is called basic response waiting time span (bRWT) herein. The bRWT has a constant value throughout a communication session.
The bRWT is communicated during the setup of a communication between initiator and target. The initiator sends a request for communication parameters, the so called Attribute Request, to the target. The target responds with an Attribute Response message containing a Timeout (TO) byte specifying the timeout value of the target for the transport protocol. The TO byte has four bits defining an integer WT, from which the bRWT is calculated asbRWT=(256×16/fc)×2WT In this equation, fc is the frequency of the operating field (the carrier frequency).
If the target needs more time than the bRWT to process an incoming request, it can send a request for an additional waiting time span, also referred to as waiting time extension, up to a number of N times the bRWT. Thus, an intermediate response waiting time span RWTINT is defined asRWTINT=bRWT×N 
According to the standard mentioned above, the factor N is defined as an integer between 0 and 59 and coded in the request by 6 Bytes called RTOX. If the target receives a so called RTOX Response message from the initiator, the initiator will wait for the response message until the end of the additional waiting time span RWTINT, counted from the transmission of the RTOX Response message. Of course, the initiator will stop waiting before the end of that time span only when it receives a next frame from the target.
While the standard allows the intermediate response waiting time span RWTINT to take on a range of values, it does not provide a way how to determine the factor N. Current NFC devices thus neither have a tool to predict the time span they need before providing a response message, nor to predict whether an extension of the bRWT will be necessary at all. Providing such tools is costly. As a consequence, it is the common practice for target devices to always request an additional waiting time span, and to always request the maximum allowable value of the parameter N (59), thus extending the waiting time span on the side of the initiator to the maximum allowable value.
Due to the half-duplex nature of the communication, which is mandatory in NFC, the initiator is not allowed to send other request messages to the target during the waiting time span, and only waits for the response message from the target. Therefore, NFC peer-to-peer communication is rather slow.
Prior art communication methods do not provide a solution that can be adapted in the present context. EP 1 009 180 A2 describes a method for managing the limited transmission capacity of a multiplexed bidirectional satellite link, i.e., a satellite channel that at the same time provides a multitude of individual communication links between a larger number of mobile stations and one base transceiver station. The transmission capacity of the satellite link is managed in order to mitigate traffic overload situations. A signaling protocol is described, which allows a transmission of user data by a mobile station only after a request for permission, which is to be granted by the base transceiver station. A mobile station repeats the request for permission if it does not receive permission within a waiting time span after the last transmission of the request. The waiting time span is mandatory for all mobile stations. In times of a high traffic load of user data over the satellite link, the usage of the satellite link for mere signaling, i.e., transmitting requests for permission, is reduced by means of communicating a larger value of the waiting time span to the mobile stations.
The method of EP 1 009 180 A2 is custom-tailored to the characteristics of a multiplexed communication link concurrently used by many devices. Application of this method to NFC communication would result in adverse effects. Instead of accelerating the half-duplex peer-to-peer NFC communication, an additional signaling protocol feature comprising the exchange of a request for permission to transmit user data and a response granting permission between NFC initiator and NFC target would introduce an extra communication delay.